Workpieces, such as semiconductor wafers or solar cells, are processed within process chambers. Workpieces are typically moved from one chamber to another by automated means. Often, each chamber must be environmentally isolated from other chambers. Consequently, the workpieces are typically moved between chambers by the use of load locks. These load locks serve to isolate a particular chamber from its outside environment. Additionally, a difference in pressure may exist on either side of the load lock. For example, near vacuum conditions may exist within the chamber, while the outside environment may be at standard atmospheric pressure. Thus, the load lock must also seal the chamber against these differences in pressure.
Load locks are used to move a workpiece from one environment to a second environment. Typically, the parameters of these two environments are different. In some embodiments, one of these two environments may be at standard pressure, while the second environment is at a much reduced pressure, such as near vacuum conditions. In some embodiments, the second embodiment has a pressure in the order of several milliTorr. For purposes of this disclosure, pressures of less than 1 Torr are referred to as vacuum conditions.
The walls of the load lock define an internal chamber, which can be isolated from both environments. The load lock includes an entry aperture, in communication with the first environment, through which workpieces may be introduced. In addition, the load lock includes an exit aperture, in communication with the second environment, through which workpieces may be extracted. The entry aperture may be an opening in one of the walls, which may be sealed by a movable door or other type of slit valve. Similarly, the exit aperture may also be an opening in one of the walls. In other embodiments, the entry or exit aperture may be incorporated into some other feature.
In operation, the load lock begins in a state where the exit aperture is closed, thereby separating the internal chamber from the second environment. The entry aperture is opened and a workpiece is placed within the chamber through the entry aperture. Typically, a mechanical apparatus, such as a robotic mechanism is used to place the workpiece in the load lock. The mechanical apparatus is removed, leaving behind the workpiece. The entry aperture is then closed, thereby sealing the internal chamber from the first environment. Typically, after the entry aperture is closed, the load lock is brought to, or near, the barometric conditions of the second environment through the introduction or exhaustion of air from the chamber. Once this operation is completed, the exit aperture is then opened and the workpiece is transferred through the exit aperture to the second environment, typically through the use of a second robotic mechanism.
Most load lock chambers have a significant volume, as it is necessary for these robotic mechanisms to reach inside the chamber to introduce and remove the workpiece. Consequently, since the volume is relatively large, the time required to remove the air from the chamber, or “pump down” the chamber, until it reaches vacuum conditions, may be significant and impact overall throughput of the processing equipment.
Therefore, it would be beneficial if there were a load lock which had a much smaller volume, thereby allowing higher throughput through the semiconductor manufacturing and handling process.